A polymer containing a color-changing molecule called a mechanophore turns red seconds before it snaps. The technology may one day allow damage to materials or structures to be easily spotted.

D. Stevenson, A. Jerez, A. Hamilton and D. Davis

The color red often means danger — and by paying attention, accidents can be prevented. At railroad crossings, flashing red lights warn cars to stay back. A red light at a traffic intersection tells cars to stop, so they don’t run into other cars. And...